Not Applicable.
Not Applicable.
1. Field of the Invention
The present invention relates generally to bioconversion of waste to useful products, and more particularly, but not by way of limitation, to methods of treating manure using anaerobic digestion.
2. Brief Description of the Art
The number and size of concentrated animal feeding operations, including agricultural operations which produce beef, pork, poultry, milk or eggs, have been steadily increasing for the past 50 years. The primary benefit of housing and feeding larger numbers of agricultural animals at a single site is that the consolidated operations give an economy of scale that lowers per unit product operating costs and improves profitability. However, as the number and size of concentrated, confined animal feeding operations has grown over the years, the development of technology to treat the waste material from these facilities has seriously lagged. The majority of the waste material from existing operations is land-applied with little treatment. Typically, manure disposal is a net cost to the animal feeding operation, and there are environmental concerns about direct application of raw manure to the ground, including rainwater runoff of pollutants into surface and ground waters and emissions of greenhouse gases to the atmosphere.
In particular, chicken egg production in the United States has undergone significant change in recent years. Such change is characterized by modest growth of the producing flock, and individual producing sites have become larger. For example, it is estimated that there are currently more than 50 egg production facilities in the United States which contain a minimum of one million laying hens. Producers have been faced with the fact that egg production and processing operations must become large and more concentrated to improve economic performance in a competitive business environment. However, of the known major producing facilities with more than one million layers, none are known to use any type of manure processing technology but rather simply apply the manure to farm ground as a method of disposal, and, as mentioned above, there are economic and environmental concerns with this method of disposing of manure generated by the egg producing operation.
Bioconversion refers to the conversion of organic matter (such as waste material) into useful products (such as usable energy) by bacterial decomposition of such organic matter. Bioconversion is also known as anaerobic digestion, which is a process utilized for pollution control in municipal sewage treatment and livestock waste handling. For example, in some cases, operators of animal feeding operations have constructed lagoons to hold manure and to allow some anaerobic digestion of the waste material before it is applied to the land. However, the condition and operation of some of these lagoons has been the subject of national news headlines, such as the breach of lagoon dikes in North Carolina and Iowa. In addition, while research by universities and government labs has shown that animal manure can be effectively treated with anaerobic digestion, poultry manure has been shown to be the most difficult to treat. Conventional anaerobic digestion technology has certain limitations in terms of reaction rates and the ability of the bacteria to be productive when conditions (such as pH, temperature and concentration of certain chemical constituents) in the digester are not optimum, and current literature teaches that anaerobic treatment of poultry manure can only be accomplished if the manure is diluted with water at a ratio of between 4 to 1 and 10 to 1. While such dilution allows for digestion of the manure, it also increases the volume of waste that must be handled and ultimately sent to disposal. As a result, this approach increases processing costs and is therefore not economic.
In spite of the efforts of the government and the animal feeding industry, there are no cost effective manure treatment facilities in operation that are not a significant and direct financial burden to the producer. Therefore, new and improved methods of treating manure using anaerobic digestion technology that overcome the disadvantages and defects of the prior art are highly desired. It is to such methods of treating manure by anaerobic digestion which not only eliminate the cost of manure disposal but also result in the production of commercially viable products that the present invention is directed.